1. Field of the Invention
The invention relates to a method for the disposal of salt-containing dusts from garbage incinerator plants.
2. Description of the Prior Art
In the cleaning process of flue gases from incinerator plants both gaseous and solid pollutants must be separated off.
The gaseous pollutants are essentially hydrogen chloride, sulfur dioxide and hydrogen fluoride and the solid pollutants fly ash containing toxic metal salts, for example the salts of lead, cadmium, chromium, mercury, tin, zinc, or their oxides or hydroxides.
For the purification of the flue gases from incinerator plants different methods are used. In these methods the purification is carried out in at least two stages; in the one stage the gaseous pollutants are separated and in a further stage the solid pollutants. To separate the gaseous and solid pollutants both wet and dry separators are employed.
Wet separator generally have a very high extraction capacity. Their disadvantage due to the process technology is however that the pollutants although separated from the air are afterwards in the water. Consequently, a further stage is necessary in order to process the pollutant-containing waste waters and this makes these methods very expensive. A further disadvantage is that slurries from the wet separation are more difficult and thus more expensive to collect, treat, transport and deposit than dusts from the dry separation.
These problems in wet flue gas purification have led in recent years to a lively development in the field of dry flue gas purification.
For dry separation of gaseous pollutants hydrated lime is blown into a reactor. The noxious gases are bound by sorption at the surface of the lime particles. In the quasi-dry method the suspension of hydrated lime is blown through jets into the reactor, the water component in the suspension having to be set so that the water can evaporate completely. The reaction products are separated in the following filter plant together with the dust particles.
In the neutralisation of acidic noxious gases by lime products the reaction compounds consist essentially of the salt calcium chloride (CaCl.sub.2), calcium sulfate as dihydrate (Ca SO.sub.4 .multidot.2H.sub.2 O) and calcium fluoride (CaF.sub.2).
In the depositing of these salt-containing dusts it is therefore to be ensured that only small salt quantities and amounts of toxic metal compounds get into the ground water, and indeed only in concentrations of the order of magnitude of the natural ground waters. These limit values are stipulated by the authorities.
The following techniques are known for depositing and treating salt-containing dusts from incinerator plants:
The salt-containing dusts are filled into tightly sealed containers and stored in an underground or aboveground dump. Storing in a suitable underground dump is admittedly very safe because the noxious substances can no longer get into the water cycle; on the other hand, this method is very expensive because the containers as well as the underground dump space and the depositing into the underground dump cause costs. Furthermore, the volume of safe underground dumps is limited and reserved for storing far more dangerous substances, in particular radioactive and highly toxic substances.
Storing dust-filled containers in aboveground dumps is no guarantee of a safe storage because firstly the containers might be damaged and secondly complete exclusion of water from an aboveground dump is not practicable.
DD-PS 149,136 describes a method for final storing of a great number of waste products which are mainly of mineral origin, usually have low water solubility and also almost all contain cement-compatible substances. These waste products are mixed with binding agents which harden by chemical rections, such as cement, lime or gypsum, or which are thermoplastic molten binders, such as bitumen, and brought into the dump area.
US-PS 3,274,784 describes a method for consolidating radioactive waste in which steps are taken which are intended to prevent the water access to the conditioning product and thus also any eluation. In this method a flowable mixture of radioactive water, cement and water is injected into a drill hole or into subterranean cavities. The drill hole or the subterranean cavity is sealed possibly before introducing the waste materials with a sealing agent, in particular cement slurries. After introducing the waste to be consolidated or solidified the filled cavities are sealed with a waste-free sealing agent, usually cement slurry.
To immobilize the salt-containing dusts as far as possible when stored in dumps it is known from DE-PS 3,545,592 by mixing with cement, water, aggregates, such as fly ash and possibly additives such as sodium sulfide, to make a waste body with edge layers which are free from special waste in that with the aid of a movable apparatus a layerwise buildup of the waste body is effected in one working operation by first forming as bottom layer a special waste-free cement/water mixture with a water/cement ratio of 0.2 to 0.8, then for building up the waste body admixing from the outside to the inside and from the bottom to the top to said cement/water mixture the special waste to be dumped with increasing concentration from 0 to 70 % by weight, simultaneously increasing the water/cement ratio to 1.2 by adding water, and subsequently in the direction towards the top layer and the lateral edge zones gradually reducing the special waste content again to 0 % by weight and reducing the water addition to return to the water/cement ratio to the previously set value between 0.2 to 0.8.
Finally, DE-PS 3,347,376 discloses a method of dumping a mixture of coal power station waste substances and waste substances from a desulfuring plant in which the mixture is mixed with addition of at least 3 % by weight hydrated lime with respect to the amount of dry residues to form a moist product which is brought to the dump and there compacted.
All the method developed so far have the disadvantages that for the stabilization valuable economic good must be used, such as bitumen and cement, in considerable proportions by weight, and secondly the limit values stipulated by the authorities are not reached in some cases. A disadvantage in the solidification during the depositing is that any defects cannot be remedied directly but only indirectly via processing of the percolating water.